Maximum deflection limiter for the control surfaces of a mobile vehicle



Oct. 2, 1956 w, ow s ET AL MAXIMUM DEFLECTION LIMlTER FOR THE CONTROLSURFACES OF A MOBILE VEHICLE Filed Jan. 23, 1952 INVENTORS CHARLES W. MCWILLIAMS CHARLES A.NIC|TA United States Patent MAXIMUM DEFLECTIONLIMITER FOR THE CONTROL SURFACES OF A MOBILE VEHICLE Charles W.McWilliams, Arlington, N. J., and Charles A. Nicita, New York, N. Y.,assignors to Bendix Aviation Corporation, Teterboro, N. J., acorporation of Delaware Application January 23, 1952, Serial No. 267,848

13 Claims. (Cl. 318-489) The present invention generally relates tocontrol apparatus for mobile vehicles and more particularly to controlapparatus for automatically limiting the displaced or applied positionof the vehicle control surface.

In mobile vehicles, such as aircraft, it is necessary to limit thelateral acceleration to which the structure of the vehicle is subjectedwhen the vehicle is turning, ascending or descending. For example, at agiven altitude and velocity, one way to limit such acceleration as, forinstance, due to a lateral turning is to limit the control surfacedeflection. If the flight velocity or ground speed is reasonablyconstant, the maximum allowable deflection is a function of the airdensity. Thus, with increasing altitude where the air becomes lessdense, the maximum allowable deflection becomes greater.

Setting the maximum control surface deflection limit for the lowestaltitude will solve the problem to some extent. However, this solutionsacrifices maneuverability at higher altitudes where a greater maximumdeflection is permissible.

An object of the present invention, therefore, is to provide novel meansfor automatically varying the maximum allowable deflection for thecontrol surface of a mobile vehicle in accordance with the parameter ofmovement or position of the vehicle.

Another object of the invention is to provide novel means to control themaximum acceleration to which the structure of a mobile vehicle issubjected when the vehicle is turning, climbing or diving.

A further object is to provide a novel steering apparatus for a vehiclein which the control signal is limited by an amount corresponding to aparameter of the movement or position of the vehicle.

A still further object is to provide a novel arrangement forcontinuously varying the maximum control of the surface of a mobilevehicle in accordance with a control parameter.

Another object is to provide a novel steering arrangement for anaircraft wherein the displacement of one or more of the craft controlsurfaces is modified in such a manner that for a given command signalless surface displacement is provided at low altitudes or high airspeedsthan at high altitude or low airspeeds.

The above and further objects and novel features of the invention willappear more fully from the following detailed description when the sameis read in connection with the accompanying drawing. It is to beexpressly understood, however, that the drawing is for the purpose ofillustration only and is not intended to define the limits of theinvention.

The single figure of the drawing constitutes a schematic diagram of oneembodiment of the present invention.

The novel lateral acceleration limiter of the present invention is shownfor the purposes of illustration and better understanding in cooperativerelationship with an automatic pilot. An embodiment of the rudderchannel of an automatic pilot of the type disclosed in co- 2,765,435Patented Oct. 2, 1956 ICC pending application Serial No. 516,488, filedDecember 31, 1943 by Paul Noxon et al., now U. S. Patent No. 2,625,348,is illustrated herein. The novel lateral acceleration limiter, however,is not limited to the particular automatic pilot or to the particularcontrol channel disclosed.

The rudder channel control for the control of the aircraft about the yawaxis, generally designated as 20, is derived from a gyro-stabilizedearth inductor compass 22 (although any heading indicator such as adirectional gyro may be used), a rate of turn gyro take-off 23, and afollow-up device 24. Compass 22 develops a signal proportional to theamount of angular displacement of the craft from a prescribed heading.This signal is fed by means of leads 25 into a stator winding 27 of aninductive device 26 that is located within a master direction indicator29. As a consequence, a directional displacement signal potential isinduced within the rotor winding 28 of inductive device 26. Thisdisplacement signal is applied to the input of a vacuum tube amplifier31 by way of lead 30. The output of amplifier 31 by means of lead 32energizes motor 33.

Motor 33 not only operates to return rotor winding 28 of inductivedevice 26 to a null position but also operates to rotate the rotorwinding 35 of a signal transmitter 34 to reproduce the directionaldisplacement signal potential within the stator winding 36 thereof. Thedirectional displacement signal potential reproduced within statorwinding 36 of signal transmitter 34 is communicated toward the rudderchannel servomotor 57 by way of lead 39.

Lead 39 is connected to the grid 40 of an amplifier tube 41. Plate 42 ofamplifier 41 is connected by lead 43 through condenser 44, by lead 45through resistor or impedance 46a, 46b, and by lead 47 to the grid 48 ofa vacuum tube amplifier 49.

Plate 50 of the latter tube 49 is coupled by lead 51 and transformer 52to lead 53 which, in turn, is connected to mixing transformer 54 foradding the signal component from follow up device 24. Transformer 54 isconnected to the input of an amplifying system 55. The output ofamplifying system 55 by means of lead 56 energizes the rudder servomotor57 to displace rudder 19.

Connected in series with the directional displacement signal by means oflead 37 is a rate of turn signal developed by the rate of turn gyrotake-01f 23 in series with stator winding 36 of signal transmitter 34.

The output of the rudder channel amplifier 55 by means of leads 56energizes a rudder servomotor 57 to displace rudder 19 through a speedreduction transmission system 58 to return the craft to its prescribedcourse. At the same time inductive follow-up device 24 is operated todevelop an electrical follow-up signal that is fed by means of a lead 59into the series circuit with the directional displacement and the rateof turn signals.

The above is, briefly outlined, a heretofore known automatic pilotsystem for one control channel of an aircraft, it being understood thatany desired trim provision may be incorporated between direction signaltransmitter 34 and the input of the servo amplifier. The novel lateralacceleration limiter of the present invention will now be described.

The voltage limiter, generally designated as 60, is fully described incopending application Serial No. 187,807, filed September 30, 1950 byMichael Kerpchar and now matured into U. S. Patent No. 2,683,226, datedJuly 6, 1954. The embodiment of the voltage limiter illustrated hereinincludes "a full wave rectifier with a transformer 61 having primarywinding 62 excited by an alternating volt age and a center-tappedsecondary winding 63. The cengreases the other side '73 of potentiometer66.

When transformer 61 is excited an alternating voltage four times theexcitation potential appears across secondary winding 63. Rectifier 69passes current during the half cycle when end 67 of secondary winding 63is positive relative to center-tap 64. Rectifier 71 passes currentduring the half cycle when end 68 of secondary winding 63 is positiverelative to center-tap 64. Accordingly, a pulsating voltage two timesthe excitation potential appears across potentiometer 66 with the side73 positive relative to side 6 An adjustable tap 75 on potentiometer 66is grounded by lead 77. Tap 75 of potentiometer 66 is positive relativeto the side 64 and negative relative to the side 73 of potentiometer 66.

Sides 6 1 and 73 are connected (1) through oppositely disposedrectifiers 80 and 81, respectively, to the output impedance 46b and lead47 and (2) through a resistor 16:: to the input lead 45 of the signalsource. Resistors 465 may be of a high value.

When a sinusoidal signal appears on lead 45, rectifier passes currentwhen lead 77 is instantaneously negative relative to side 73 ofpotentiometer 66. Such current flow occurs only when the signal voltageis instantaneously greater than the excitation voltage appearing attransformer The excitation voltage and the'signal voltage must be inphase or 180 degrees out of phase with one another. in other words, thenulls of the excitation voltage and the signal voltage must occursimultaneously, otherwise the output vo-ltage communicated by lead 47will be distorted. The amplitude of the excitation voltage determinesthe limit of the output voltage.

When the amplitude of the signal potential is below the limiting value,then no current flows in the circuit including rectifier-s 30, 81,potentiometer 66, and lead 77. The output voltage under this conditionis identical to the signal input and appears at output lead 47.

When the amplitude of the signal exceeds the limiting value asdetermined by the excitation voltage, then current flows through theabove circuit including rectifier 80 or rectifier 81 as determined bythe phase of the input signal voltage. The output potential isrestricted to the limiting value set by the excitation potential becauseof the voltage drop across resistor 46. Rectifiers 80 and 31, in effect,short circuit the portion of the signal which exceeds the limitingvalue.

In the embodiment illustrated herein, the excitation potential for thelimiter is controlled as a function of ambient pressure conditions.Ambient pressure conditions as used herein are intended to include notonly pressure changes due to varying craft altitude levels but also dueto changes in the speed of the craft, etc. For example, a change inambient pressure may occur as a result of chang in craft altitude;again, a change in ambient pressure may occur as a result of the dynamiceffect of a crafts movement through the air without a change inaltitude.

Referring, now, to the drawing, the excitation potential for the limiteris controlled as a function of ambient pressure conditions due to achange in altitude, the ambient pressure condition being sensed by abarometric device.

As shown diagrammatically, the altitude control unit, generallydesignated as 99, comprises a bellows 100 mounted for expansion andcontraction within a casing 161. The interior of the bellows is indirect communication with static pressures by way of a conduit 102. Theinterior of the casing is in communication with static pressure by wayof a conduit 103. Normally, therefore, the bellows 100 is centered sinceit is exposed to static pressure on both sides.

Under certain conditions, the communication of static pressure to thecasing 101 may be closed. To this end a suitable solenoid operated valve104 is provided within the conduit 103. The solenoid comprises a coil10S connected for energization with a battery 106 through a switch 107.An armature 108 is provided adjacent the coil and operatively connectedwith the valve. A spring 109 urges the armature in one direction to openthe valve 1"4 when the switch 107 is open and the coil deenergized andin an opposite direction to close the valve when the switch is closedand the coil energized.

When the switch 107 is closed, therefore, any change in static pressuresuch as that due to altitude changes is communicated to the interior ofthe bellows 100. Air of a selected density has been locked in casing101. Accordingly, the bellows expands or contracts depending uponwhether the external pressure rises o-r drops. Motion of the bellows istransmitted through a shaft 110 to a linearly dispiaceable winding 111.

Winding 111 is connected for energization with a suitable source ofcurrent. Winding 111 is normally centered with regard to a pair ofwindings 112 and 113 which are connected in series opposed relation.Thus with the movable, current conducting winding 111 centered, equaland opposite voltages are induced within windings 112, 113 and their netvalu is zero. However, motion of the movable winding 111 from itscentral or null position induces more voitage in one of the windings 112and 113 and less in the other. Consequently, a differential exists andcurrent will flow in one direction or another.

A pressure sensing device of the above type is more fully described inU. S. Patent No. 2,474,618 granted lune 28, 1949 to Richard L. Divoll.However, the invention is not limited to this pressure sensing device asobviously various other conventional barometric devices or altimetersmay be used.

One end of winding 112 is grounded. Lead 11 i connects one end ofWinding 113 to the input of an amplifier system 115. The output ofamplifier 115 is connected by leads 116 for the energization of aservomotor 117. Servomotor 117 is mechanically connected at 113 to tap119 and at .123 to windings 112 and 113.

When a voltage differential exists between windings 112 and 113, acurrent flows through lead 114, is amplitied at 115, and energizesservomotor 117. As servomotor 117 operates it moves windings 112 and 113to a new null point or position relative to displaceablc winding 111where no differential exists between windings 112 and 113. At the timeservomotor 117 moves tap 119 to its new position on resistor 130,

Tap 119 is the take-off for a potentiometer comprised of (l) a resistorhaving one end connected by a lead 130a to the ground junction of theprimary winding 62 of transformer 61 and the other end energized by somesuitable alternating power source and (2) a take-off 119 connected by alead 131 to the other end of primary winding 62. Primary winding 62supplies the excitation potential to the limiter 60.

Operation Closing switch 107 energizes relay coil 105 closing valve 104and locking the air in casing 101. This procedure may be carried outprior to craft take-off. Pres sure changes in the air of the atmosphereare communicated by conduit 102. to the bellows 100 causing them toexpand or contract. This bellows movement results in movement of rod 110and Winding 1-11, upsetting the balanced condition of the series opposedcoils 112 and 113.

The current caused by the voltage differential in wind ings 112 and 113,amplified by amplifier system 115, drives servomotor 117 until windings112 and 113 reach a null point again. Operation of servomotor 117 alsomoves tap 119 along resistance 130 to vary the potential across winding62.

The amplitude of the signal appearing in lead 47, which constitutes theultimate command signal communicated to the rudder servo amplifier,depends upon the excitation potential of limiter 60. The excitationcurrent for this limiter is supplied by transformer 61. Therefore, sincethe excitation potential is controlled by a device 99 responsive to aparameter of movement of the vehicle and the excitation potentialcontrols the signal strength in conductor 47, then the signal strengthis a function of the parameter to which device 99 responds which, inthis embodiment is altitude as sensed by air density.

The signal in lead 47 is an exact reproduction of the automatic controlcommand signal from the sensor pickotfs 23 and 36. The signal, however,is on a scale limited by limiter 60.

When the air is dense, i. e., during craft flight at low altitudes, thesignal from lead 39 that appears in lead 47 is limited to a smallmagnitude. Consequently, the maximum allowable deflection of the ruddercontrol is small. Tap 119 is in such a position with respect to resistor130 that only a small excitation potential appears at primary winding 62of transformer 61. This excitation potential limits the value of thesignal appearing in lead 47. When the ultimate command signal appearingon lead 45 is greater than the limiting value as determined by theexcitation potential at winding 62 of transformer 61, rectiflers S or81, depending upon the phase of the signal, operate to short circuit, ineffect, that portion of the command signal which exceeds the limitingvalue through potentiometer 66 and tap 75 to ground lead 77. Of course,when the command signal potential appearing at lead 45 is less than thelimiting value, the signal potential appearing at lead 47 is identicalto the signal appearing at lead 45 and no current flows in the circuitincluding rectifiers 80, 81, potentiometer 66, tap 75, and lead 77.

As the aircraft ascends, for example, to higher altitudes where theatmosphere is rarified, the maximum allowable deflection of the controlsurface becomes greater. Pressure changes cause movement of shaft 110and winding 111. This causes a differential voltage to exist in windings112 and 113. The differential voltage energizes servomotor 117 to movewindings 112 and 113 to a new null position and simultaneously moves tap119 on resistor 13%. The new position of tap 1 19 allows a greaterpotential to be applied to Winding 62. Consequently, a greater commandsignal can appear in lead 45 and in lead 47 before any portion of thecommand signal is short circuited. The greater amplitude of the commandsignal, of course, results in a greater maximum deflection of thecontrol surface.

In the embodiment described above, the lateral acceleration has beenlimited by limiting the maximum allowable deflection of the controlsurface as a function of one flight parameter of the vehicle-altitude,herein measured by a barometric device. It is obvious, however, that thenovel arrangement is not restricted to altitude but may be used withindicators of other parameters such as airspeed, ground speed, etc. Withan airspeed indicator for example, the resistor 130 and tap 119 would beso positioned as to diminish the maximum allowable deflection of thecontrol surface with increase in airspeed.

The foregoing arrangement provides a novel means for continuouslylimiting a command signal for the control of a vehicle in response to acorresponding condition which the vehicle encounters. In the illustratedembodiment, the maximum allowable deflection of the craft controlsurface is varied continuously as the density of the air change when theaircraft ascends or descends.

While only one embodiment has been illustrated and described, variouschanges may also be made in the design and arrangement of partsillustrated without departing from the spirit and scope of theinvention, as will now be understood by those skilled in the art.

We claim:

1, In apparatus of the class described, an impedance constituting aninput for receiving a command signal, an impedance constituting anoutput for producing a voltage corresponding to said command signal, aservomotor responsive to said output voltage, a limiter means connectingsaid input and output for limiting the maximum magnitude of said outputvoltage, and a means responsive to ambient pressure conditions formodifying the limiting action of said limiter means so that the maximummagnitude of said output voltage varies as a function of ambientpressure condition.

2. An acceleration limiter for an aircraft having control surfacesthereon displaceable by a servomotor, comprising reference means fordeveloping a control signal for said servomotor corresponding to craftdeviation from a predetermined reference, and means connecting saidreference means and said servomotor including limiter means for limitingthe magnitude of said control signal, and a means responsive to ambientpressure conditions for modifying the action of said limiter means sothat the maximum signal to said servomotor varies as a function ofambient pressure.

3. In an automatic steering system for a mobile vehicle, reference meansfor generating signals corresponding to vehicle departure from apredetermined reference for controlling said vehicle, limiter meansconnected to receive said signals for limiting the magnitude of thelatter, and a means responsive to a predetermined flight parameter ofthe vehicle to modify the action of said limiter so that for the samedeparture from a predetermined reference, the maximum signal to saidservomotor is varied as a function of said parameter.

4. In an automatic steering system for a mobile vehicle, a signaldeveloping means for developing a control signal for said vehicle, saidsignal corresponding in sense and magnitude to the displacement of thevehicle from a predetermined reference, a limiter means connected toreceive said signal and responsive to a predetermined flight parameterof the vehicle for limiting the magnitude of said signal, and aservomotor responsive to said limiter signal for controlling saidvehicle, said limiter means including a means to shunt the portion ofsaid control signal exceeding a predetermined magnitude and meansresponsive to said parameter for operating said shunting means as afunction of said parameter.

5. In an automatic pilot for aircraft, reference means for developing asignal to control the aircraft, a limiter means connected with thereference means to limit the control signal magnitude including a pairof rectifiers adapted to shunt the portion of said signal that exceeds apredetermined amount, and a means responsive to a flight parameter ofsaid craft to vary the shunting action of said rectifiers and therebythe limiting action of said limiter means so that the magnitude of thecontrol signal varies as a function of said parameter.

6. In steering apparatus for a mobile vehicle, reference means fordeveloping signals to control the course of said vehicle, a limiterconnected to receive said signals for limiting the magnitude of saidsignals and a means responsive to a flight parameter of said vehicle tochange the limits of magnitude of said signals as a function of saidparameter.

7. An automatic pilot for an aircraft having a displaceable controlsurface, comprising reference means for developing a command signaladapted to displace said surface an amount corresponding to theamplitude of said signal, means connected to receive said signal which,when operated, varies the maximum amplitude of said signal, and meansconnected with said signal varying means for operating the latter inaccordance with ambient pressure changes whereby the maximumdisplacement of said surface for a predetermined command signal isvaried as a. function of ambient pressure.

8. An automatic pilot for an aircraft having a displaceable controlsurface, comprising reference means for developing a command signal, aservomotor for displacing said surface an amount corresponding to theamplitude of said signal, limiting means interconnecting said referencemeans and said servornotor for receiving said signal, said limitingmeans including a pair of rectifiers having an energization appliedthereto and adapted to shunt the portion of said control signal thatexceeds a predetermined amount and being adapted for variableenergization to thereby vary the amplitude of said signal, and ambientpressure change responsive means connected with said limiting means forvariably energizing the latter.

9. An automatic steering system for an aircraft comprising referencemeans for generating a signal corresponding to departure of the craftfrom a predetermined reference, a servomotor for controlling the craft,and means interconnecting said reference means and said 8131' vomotorfor operating the latter by said signal including a limiter means forsaid signal, said limiter means having a pair of rectifiers connectedacross said interconnecting means in parallel circuits with thepolarities the rectifiers in the circuits opposite, a variable strengthalternating current source connected with said rectifier-s so as tooppose current flow through said circuits, and means responsive to aflight parameter of said craft for varying the strength of said source.

10. in an automatic pilot for mobile craft having a control surfacethereon actuated by a servomotor for controlling the attitude of saidcraft, means for developing a command signal corresponding to thedeviation of the craft from a predetermined attitude, and means fortransmitting said signal to said servomotor including impedanceconstituting an input for receiving said command signal, an impedanceconstituting an output for producing a signal corresponding to saidcommand signal for controlling said servomotor, limiter means connectingsaid input and output for limiting the magnitude of the signal at saidoutput, whereby the change in attitude may not be so great as to imposestresses on the craft exceeding a safe limit, and means responsive toambient pressure conditions for modifying the limiting action of saidlimiter means so that the maximum signal at said output varies as afunction of ambient pressure.

11. A system for operating the control surface of an aircraft,comprising a servomotor for positioning said surface With respect tosaid aircraft, signal means for developing a command signal for saidservomotor, and transmission means connecting said signal means and saidservomotor and having an input for receiving said signal, an output fordelivering to said servomotor a signal voltage corresponding to saidcommand signal, and limiter means for limiting the magnitude of thesignal delivered at said ouptut including a pair of rectifiers forshunting a portion of the command signal when it exceeds a predeterminedmagnitude, and a means responsive to ambient pressure conditions formodifying the action of said limiter means by changing the bias on saidrectifiers, whereby the maximum signal is varied as a function ofambient pressure.

12. In an automatic steering system for a craft, reference means fordeveloping a control signal Whose amplitude and phase vary with thesense and magnitude of deviation of the craft from a predeterminedreference, a servomotor for controlling said craft to correct for thedeviation, and means for connecting said reference means and saidscrvomotor for controlling the latter by the forme said connecting meansincluding a pair of biased rectificrs adapted to shunt the portion ofsaid signal that exceeds a predetermined amplitude, and means responsiveto a flight parameter of said craft for varying the bias of saidrectifiers, whereby the maximum signal received by said servomotor isvaried as a function of said parameter.

13. In apparatus of the class described, an impedance constituting aninput for receiving a signal corresponding to the extent of deviationfrom a predetermined heading, an impedance constituting an output forproducing an output voltage corresponding to the signal but of limitedmaximum magnitude, a limiter means connected with said input and outputfor limiting the maximum magnitude of said output voltage, and a meansresponsive to ambient pressure conditions for modifying the limitingaction of said limiter means so that the maximum magnitude of saidoutput voltage is varied as a function of ambient pressure.

References Cited in the file of this patent UNITED STATES PATENTS2,356,339 Morrison Aug. 22, 1944 2,387,795 Isserstedt Oct. 30, 19452,450,907 Newton et al. Oct. 12, 1948 2,474,618 Divoll June 28, 19492,511,846 Halpert June 20, 1950 2,552,348 Shapiro et a1. May 8, 19512,608,351 Smoot Aug. 26, 1952

